1. Field of the Invention
The present invention relates to the preparation of silane, and, more especially, to the preparation of silane from halogenosilanes.
2. Description of the Prior Art
It is of course well known to this art that silane constitutes a preferred starting material for the preparation, by decomposition, of silicon which is particularly useful for the fabrication of semiconductor devices or photovoltaic devices (solar cells).
It too is known to this art that it is possible to obtain silane by the dismutation of trichlorosilane in the presence of various catalysts, according to the following equilibrium reactions: EQU 2HSiCl.sub.3 .revreaction.H.sub.2 SiCl.sub.2 +SiCl.sub.4 ( 1) EQU 2H.sub.2 SiCl.sub.2 .revreaction.HSiCl.sub.3 +H.sub.3 SiCl (2) EQU 2H.sub.3 SiCl.revreaction.SiH.sub.4 +SiCl.sub.2 ( 3)
namely, on an overall basis: EQU 4HSiCl.sub.3 .revreaction.SiH.sub.4 +3SiCl.sub.4. (4)
Thus, according to French Pat. No. 2,261,977, it has been proposed to produce silane by the dismutation reaction or redistribution reaction of HSiCl.sub.3 in a bed of solid anion-exchange resin, at a sufficient temperature to cause the reaction products of lower boiling point to vaporize out of the reaction zone, and to cause the liquid reaction product of higher boiling point, SiCl.sub.4, to condense and to flow away from the reaction zone. The temperature at the top of the bed is maintained at a value above the boiling point of SiH.sub.4 and below the boiling point of H.sub.3 SiCl, and SiH.sub.4 containing small amounts of hydrogenochlorosilanes, which require subsequent separation, is recovered from the bed.
This particular process, which is extremely complicated and difficult to carry out, either involves the continuous distillation of the products of the various equilibrium reactions (1), (2) and (3) and permits a degree of separation of the various products present, or involves the purification of SiH.sub.4 on a charcoal trap.
Furthermore, differemt processes are also known for the preparation of dichlorosilane by the dismutation of trichlorosilane in the presence of various catalysts. In this dismutation according to the aforesaid reaction (1), the other chlorinated silanes are also obtained in certain cases, in very low proportions, the yields of obtained dichlorosilane always being much greater than the yields of the other chlorosilanes. Among such catalysts heretofore known for this purpose, the following are particularly representative: tertiary amines of the general formula NR'R"R'", in which R', R" and R'" are identical or different alkyl radicals (French Pat. No. 1,111,925), amine hydrochlorides (French Pat. No. 2,096,605), N-substituted pyrrolidones (French Pat. No. 2,290,447) and tetraalkylureas (French Pat. No. 2,290,448). Cf. French Pat. No. 2,118,725.